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    SubjectRe: [PATCH v7 3/3] perf-stat: enable counting events for BPF programs
    Em Tue, Jan 19, 2021 at 11:42:49AM -0300, Arnaldo Carvalho de Melo escreveu:
    > Em Tue, Jan 19, 2021 at 11:31:44AM -0300, Arnaldo Carvalho de Melo escreveu:
    > > Em Tue, Jan 19, 2021 at 12:48:19AM +0000, Song Liu escreveu:
    > > > > On Jan 18, 2021, at 11:38 AM, Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
    > > > We are looking at two issues:
    > > > 1. Cannot recursively attach;
    > > > 2. prog FD 3 doesn't have valid btf.
    >
    > > > #1 was caused by the verifier disallowing attaching fentry/fexit program
    > > > to program with type BPF_PROG_TYPE_TRACING (in bpf_check_attach_target).
    > > > This constraint was added when we only had fentry/fexit in the TRACING
    > > > type. We have extended the TRACING type to many other use cases, like
    > > > "tp_btf/", "fmod_ret" and "iter/". Therefore, it is good time to revisit
    > > > this constraint. I will work on this.
    >
    > > > For #2, we require the target program to have BTF. I guess we won't remove
    > > > this requirement.
    >
    > > > While I work on improving #1, could you please test with some kprobe
    > > > programs? For example, we can use fileslower.py from bcc.
    >
    > > Sure, and please consider improving the error messages to state what you
    > > described above.
    >
    > Terminal 1:
    >
    > [root@five perf]# perf trace -e 5sec.c
    > ^C
    > [root@five perf]# cat 5sec.c
    > #include <bpf.h>
    >
    > #define NSEC_PER_SEC 1000000000L
    >
    > int probe(hrtimer_nanosleep, rqtp)(void *ctx, int err, long long sec)
    > {
    > return sec / NSEC_PER_SEC == 5;
    > }
    >
    > license(GPL);
    > [root@five perf]# perf trace -e 5sec.c/max-stack=16/
    > 0.000 sleep/3739435 perf_bpf_probe:hrtimer_nanosleep(__probe_ip: -1743337312, rqtp: 5000000000)
    > hrtimer_nanosleep ([kernel.kallsyms])
    > common_nsleep ([kernel.kallsyms])
    > __x64_sys_clock_nanosleep ([kernel.kallsyms])
    > do_syscall_64 ([kernel.kallsyms])
    > entry_SYSCALL_64_after_hwframe ([kernel.kallsyms])
    > __clock_nanosleep_2 (/usr/lib64/libc-2.32.so)
    >
    >
    > Terminal 2:
    >
    > [root@five ~]# perf stat -e cycles -b 180 -I 1000
    > libbpf: elf: skipping unrecognized data section(9) .eh_frame
    > libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
    > perf: util/bpf_counter.c:227: bpf_program_profiler__read: Assertion `skel != NULL' failed.
    > Aborted (core dumped)

    Out to lunch, will continue later, but this may help you figure this out
    till then :)

    Starting program: /root/bin/perf stat -e cycles -b 244 -I 1000
    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib64/libthread_db.so.1".

    Breakpoint 1, bpf_program_profiler_load_one (evsel=0xce02c0, prog_id=244) at util/bpf_counter.c:96
    96 {
    (gdb) n
    104 prog_fd = bpf_prog_get_fd_by_id(prog_id);
    (gdb)
    105 if (prog_fd < 0) {
    (gdb)
    109 counter = bpf_counter_alloc();
    (gdb)
    110 if (!counter) {
    (gdb) n
    115 skel = bpf_prog_profiler_bpf__open();
    (gdb) p counter
    $9 = (struct bpf_counter *) 0xce09e0
    (gdb) p *counter
    $10 = {skel = 0x0, list = {next = 0xce09e8, prev = 0xce09e8}}
    (gdb) p *counter
    $11 = {skel = 0x0, list = {next = 0xce09e8, prev = 0xce09e8}}
    (gdb) n
    libbpf: elf: skipping unrecognized data section(9) .eh_frame
    libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) .eh_frame
    116 if (!skel) {
    (gdb)
    121 skel->rodata->num_cpu = evsel__nr_cpus(evsel);
    (gdb)
    123 bpf_map__resize(skel->maps.events, evsel__nr_cpus(evsel));
    (gdb)
    124 bpf_map__resize(skel->maps.fentry_readings, 1);
    (gdb)
    125 bpf_map__resize(skel->maps.accum_readings, 1);
    (gdb)
    127 prog_name = bpf_target_prog_name(prog_fd);
    (gdb)
    128 if (!prog_name) {
    (gdb)
    133 bpf_object__for_each_program(prog, skel->obj) {
    (gdb)
    134 err = bpf_program__set_attach_target(prog, prog_fd, prog_name);
    (gdb)
    135 if (err) {
    (gdb)
    133 bpf_object__for_each_program(prog, skel->obj) {
    (gdb) p evsel
    $12 = (struct evsel *) 0xce02c0
    (gdb) p evsel->name
    $13 = 0xce04e0 "cycles"
    (gdb) n
    134 err = bpf_program__set_attach_target(prog, prog_fd, prog_name);
    (gdb)
    135 if (err) {
    (gdb)
    133 bpf_object__for_each_program(prog, skel->obj) {
    (gdb)
    141 set_max_rlimit();
    (gdb)
    142 err = bpf_prog_profiler_bpf__load(skel);
    (gdb)
    143 if (err) {
    (gdb)
    148 assert(skel != NULL);
    (gdb)
    149 counter->skel = skel;
    (gdb)
    150 list_add(&counter->list, &evsel->bpf_counter_list);
    (gdb) c
    Continuing.

    Breakpoint 4, bpf_program_profiler__install_pe (evsel=0xce02c0, cpu=0, fd=3) at util/bpf_counter.c:247
    247 {
    (gdb) n
    252 list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
    (gdb)
    253 skel = counter->skel;
    (gdb) watch counter->skel
    Hardware watchpoint 6: counter->skel
    (gdb) p counter->skel
    $14 = (void *) 0xce0a00
    (gdb) n
    254 assert(skel != NULL);
    (gdb) p skel
    $15 = (struct bpf_prog_profiler_bpf *) 0xce0a00
    (gdb) c
    Continuing.

    Hardware watchpoint 6: counter->skel

    Old value = (void *) 0xce0a00
    New value = (void *) 0x0
    0x00000000005cf45e in bpf_program_profiler__install_pe (evsel=0xce02c0, cpu=0, fd=3) at util/bpf_counter.c:252
    252 list_for_each_entry(counter, &evsel->bpf_counter_list, list) {
    (gdb) info b
    Num Type Disp Enb Address What
    1 breakpoint keep y 0x00000000005ceb44 in bpf_program_profiler_load_one at util/bpf_counter.c:96
    breakpoint already hit 1 time
    2 breakpoint keep y 0x00000000005cef2e in bpf_program_profiler__enable at util/bpf_counter.c:192
    3 breakpoint keep y 0x00000000005cf00a in bpf_program_profiler__read at util/bpf_counter.c:208
    4 breakpoint keep y 0x00000000005cf3ba in bpf_program_profiler__install_pe at util/bpf_counter.c:247
    breakpoint already hit 1 time
    5 breakpoint keep y 0x00000000005ce8d4 in bpf_program_profiler__destroy at util/bpf_counter.c:47
    6 hw watchpoint keep y counter->skel
    breakpoint already hit 1 time
    (gdb) p evsel
    $16 = (struct evsel *) 0xce02c0
    (gdb) bt
    #0 0x00000000005cf45e in bpf_program_profiler__install_pe (evsel=0xce02c0, cpu=0, fd=3) at util/bpf_counter.c:252
    #1 0x00000000005cf4f3 in bpf_counter__install_pe (evsel=0xce02c0, cpu=0, fd=3) at util/bpf_counter.c:276
    #2 0x00000000004f3ef1 in evsel__open_cpu (evsel=0xce02c0, cpus=0xce0500, threads=0xce75c0, start_cpu=0, end_cpu=1) at util/evsel.c:1792
    #3 0x00000000004f4aa7 in evsel__open_per_cpu (evsel=0xce02c0, cpus=0xce0500, cpu=0) at util/evsel.c:1996
    #4 0x000000000057f6f2 in create_perf_stat_counter (evsel=0xce02c0, config=0xa97860 <stat_config>, target=0xa97660 <target>, cpu=0) at util/stat.c:568
    #5 0x0000000000435d96 in __run_perf_stat (argc=0, argv=0x7fffffffdb60, run_idx=0) at builtin-stat.c:790
    #6 0x00000000004367e3 in run_perf_stat (argc=0, argv=0x7fffffffdb60, run_idx=0) at builtin-stat.c:1001
    #7 0x0000000000439e35 in cmd_stat (argc=0, argv=0x7fffffffdb60) at builtin-stat.c:2415
    #8 0x00000000004cf058 in run_builtin (p=0xaabe00 <commands+288>, argc=7, argv=0x7fffffffdb60) at perf.c:312
    #9 0x00000000004cf2c5 in handle_internal_command (argc=7, argv=0x7fffffffdb60) at perf.c:364
    #10 0x00000000004cf40c in run_argv (argcp=0x7fffffffd9ac, argv=0x7fffffffd9a0) at perf.c:408
    #11 0x00000000004cf7d8 in main (argc=7, argv=0x7fffffffdb60) at perf.c:538
    (gdb) n
    261 return 0;

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